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The Eighteenth Amendment of the Constitution of Ireland permitted the state to ratify the Amsterdam Treaty. It was effected by the Eighteenth Amendment of the Constitution Act, 1998, which was approved by referendum on 22 May 1998 and signed into law on the 3 June of the same year.

Changes to the text[]

  • Insertion of new Article 29.4.5:
The State may ratify the Treaty of Amsterdam amending the Treaty on European Union, the Treaties establishing the European Communities and certain related Acts signed at Amsterdam on the 2nd day of October, 1997.
  • Insertion of new Article 29.4.6:
The State may exercise the options or discretions provided by or under Articles 1.11, 2.5 and 2.15 of the Treaty referred to in subsection 5° of this section and the second and fourth Protocols set out in the said Treaty but any such exercise shall be subject to the prior approval of both Houses of the Oireachtas.
  • (Existing subsections 5 and 6 of Article 29.4 are retained but renumbered as subsections 7 and 8 respectively)


The Eighteenth Amendment of the Constitution was one of a number of amendments that have been made to expressly permit the state to ratify changes to the founding treaties of the European Union (others have been the Tenth, Eleventh and Twenty-sixth Amendments). These amendments have all been adopted in response to the 1987 ruling of the Supreme Court, in the case of Crotty v. An Taoiseach, that major changes to the treaties are unconstitutional unless accompanied by an amendment. However it has been a matter of scholarly dispute as to whether or not every one of these treaties has been sufficiently far-reaching as to actually necessitate a constitutional amendment. The Treaty of Amsterdam contained a number of optional protocols that member-states could activate at a later time after its adoption. The Eighteenth Amendment permitted the Republic to choose to exercise these options, provided it had the support of the Oireachtas (parliament). While the changes shown above are those made to the English-language version of the constitution, constitutionally it is the Irish text that takes precedence.

The Eighteenth Amendment was introduced by the Fianna FáilProgressive Democrats coalition government of Bertie Ahern and was also supported by Fine Gael and the Labour Party (the two major opposition parties). The referendum on the amendment occurred on the same day as the referendum on the Nineteenth Amendment, which related to the Good Friday Agreement. The Eighteenth Amendment was approved by 932,632 (61.7%) votes in favour to 578,070 (38.3%) against, a narrower margin than in previous referendums on the European Union


Eighteenth Amendment of the Constitution of Ireland referendum
Choice Votes Percentage
Referendum passed Yes 932,632 61.74%
No 578,070 38.26%
Valid votes 1,510,702 97.85%
Invalid or blank votes 33,228 2.15%
Total votes 1,543,930 100.00%
Voter turnout 56.20%
Electorate 2,747,088